Panfleto appears in several bilingual dictionaries translated literally as “pamphlet.” But “pamphlet” is more appropriately folleto while, at least in Spain, panfleto is something quite different. Indeed, as defined in the DLE, panfleto denotes libelo difamatorio or an opúsculo de carácter agresivo. Fundéu likewise distinguishes between the two, indicating that “folleto” es una obra impresa, no periódica, de reducido número de hojas, while “panfleto” siempre tiene sentido difamatorio. Indeed, the term panfleto is often associated with political propaganda (un panfleto político) and is defined as such (papel o folleto de propaganda política) in Clave.* Thus the informal expression nos echó un panfleto implies “(he/she) subjected us to a (political) diatribe.” And the adjectives panfletario/a (estilo propio de los panfletos) and the noun panfletista (autor de un panfleto) also have this meaning. Thus “pamphlet” should be rendered as folleto rather than panfleto, unless the reference is to some sort of biased, partisan or propagandistic writing.
*Clave: Diccionario de uso del español actual. Ediciones SM, 2006.